PC ISA Card Pinout and Board Size

The PCXT bus uses the J1 A/B rows, and a PCAT bus [ISA Bus] uses the J1 [A/B rows] and J2 [C/D rows] connectors. The fingers are copper strips on the PWB spaced on 0.1 inch centers. The PCAT bus was an up-grade to the original PCXT bus. The Pin-Out for both bus types are shown in the table below. The connector positions and relationship to the board are shown in the two figures at the top of the page. Both figures show a PCAT card, but the first figure also shows an attached PCI bus. Example dimensions for the card sizes are provided. Some of the signal names provided in the pin-out table are not correct terms. For example the Address lines called out above would be called SA# [SA19 - SA0], and the Data lines would be called SD# [SD15 - SA0]. The IBM compatible AT card [ISA] used the standard (edge) connector provided by the XT bus and added an additional edge connector behind that with the same pin-spacing @ 0.1 inch center-to-center. The additional connector has only 36 fingers (18 per side), while the XT connector had 62 fingers (32 per side). The Personal Computer Motherboard could then accept either an 8 or 16 bit card in an 8 bit slot (XT), or (if the connector was provided) a 16 bit card in an AT slot. A maximum number of 8 Expansion slots were provided on IBM compatible Motherboards. The ISA clock ran at around 10MHz. The ISA bus is obsolete and should not be used with new computer systems.